1. Field of the Invention
The present invention relates to the creation, extraction and high throughput delivery of very fine mist for humidification, fire suppression, blast mitigation or other chemical applications. In particular, the invention pertains to generating a mist containing very fine droplets at ambient pressure from a reservoir of water or liquid, and, then, effectively aerosolizing very fine droplets from the mist using swirl or helical flow behavior for delivery with sufficiently high throughput for effective application.
2. Description of the Prior Art
Previously, ultrasonic transducer devices have been used in small-scale mist generation units to generate mists for familiar purposes such as medical inhalers and decorative fountains in indoor-outdoor applications. These small-scale mist generation units would produce from 5-10 ml/min of liquids. Due to demand for high throughput mist generators in recent years, significant improvement ensued in humidification applications by implementing systems with linearly arranged arrays of piezoelectric transducers to multiply the total throughput.
However, the mists generated from these prior high throughput units generally comprise both small and larger droplets, mostly greater than several microns in size due to the methods utilized in extraction and transport of the mist formed in the mist generating unit. For instance, existing high-throughput humidifier designs use a fan or fans to directly push the mist upwards out of the container from behind the transducers. In these designs where mist is driven out of the misting chamber by a fan, large droplets of mist fall back into the liquid reservoir. However, the direct air current impinging on the water fountain in these humidifiers further forces the mist coming out of the humidifier to contain large proportions of the more coarse water droplets found in the center of the mist fountain. These impinging airflow-based systems transport significant amount of moisture due to forced convection currents. Thus, the final mist still contains coarser droplets. Moreover, residence time of the mist and carrier in the misting chamber is too short and not favorable for stable aerosol formation.
U.S. Pat. Nos. 5,300,260 and 5,922,247 provide examples of current technology for existing high-throughput humidifier designs. U.S. Pat. No. 5,300,260 to Keshet et al. uses multiple transducer units arranged in a circular geometry to achieve higher throughput. In Keshet air is passed through a central tube, and the flow of air is deflected by a domed-shaped top-hat back into the mist chamber or reservoir. The air flow directly impinges on the misting region and picks up mist and carries upwards. No special separation device is implemented for separation of coarser mist droplets not large enough to fall back into the fountain. In another embodiment, air is passed through tubes surrounding individual transducers. This air carries the mist upwards. Again, the device has not means of achieving optimum aerosol formation or separation of coarser droplets, and airflow directly impinging from above on the mist formation region would negatively affect optimum aerosol formation and separation.
U.S. Pat. No. 5,922,247 to Shoham et al. uses multiple transducer arrays to achieve increased mist throughput and the use of a high velocity air stream to first push the mist from the production chamber to a common chamber. Shoham briefly mentions the post-processing of the mist driven out of the misting chamber by forced convection using high velocity air and then again using high velocity air to produce a cyclone action and using inertial separation to separate larger droplets. The high velocity jet of air impinging on the sides of the conical chamber would collapse or vaporize mist droplets, and the high-speed inertial separation would cause vaporization or condensation surface shearing action. Thus, the transport and post-processing of the mist would cause significant loss of mist by coalescence and condensation into liquids.
As a result, these mists created by prior mist generators include many shortcomings that are disadvantageous for humidification and other applications. Additionally, maximum throughput reportedly generated by prior methods of has been limited to about 0.25 liter per minute (Lpm) and uses generating apparatus of unacceptably large physical size and high cost.
The shortcomings of mist droplets greater than several microns (referred to herein as large droplets) include that the droplets collapse easily due to coalescence and drop out to form liquids without reaching their intended target point or spaces. These large droplets are obstructed by physical objects and condense and drop out and, thus, do not display gas-like flow behavior, which causes crack and crevices and other areas to remain unaffected by the mist. Dropping out and condensation causes the amount of liquid needed in applications to be very high, which also leads to leaving the areas treated damp because of deposited liquid causing collateral damage in the area treated.
In specific applications such as humidification, fire suppression and blast mitigation, fast vaporization of extremely small droplets is an important property for providing an efficient cooling process. In recent studies, the inventors have observed that in sub-micron diameter droplets reaching nanometer scale the molecules in each droplet tend to migrate towards the surface of the droplet making the droplet very reactive for several applications. Thus, the need has been discovered for efficient aerosol formation, extraction, separation and delivery of mist from the mist fountain chamber, whereby the delivered mist is formed of extremely small droplets.